How can anyone believe these Polls. I have never been asked for an opinion, those that I've seen being ?polled are often dressed like the radical elements of society and obviously have too much time on their hands to stop for half an hour or so?

The short answer is that some are better than others, and take all of them with a pinch of salt.

Political polls like this are never taken in the street, they are done over the phone, or increasingly by email. The methodology is very complex, and then weightings are applied by age, region, etc.

Polls for different papers tend to reflect at least partially the political affiliations of that paper. ICM in the Indie are notorious for overestimating Labour support and downplaying Tory support when their findings are compared against actual results.

Whilst I would agree with you that they are only ever a sanpshot and not to be relied upon completely, I don't think that they are valueless.

Interestingly, YouGov polls these days are frighteningly accurate when compared against actual results. Psephology is increasingly an actual science and not a marketing trick.